A variety of methods and processes are described in the patent literature for the treatment and recovery of arsenic from ores and dusts. Many of these apply a caustic or alkali extraction.
U.S. Pat. No. 1,243,323 discloses the reaction of smelter dusts with calcium hydroxide for recovery of arsenic containing compounds that are useful as insecticides.
U.S. Pat. No. 1,504,627 is directed toward a process for the treatment of arsenate ores to produce water soluble arsenates by treating the ore with a caustic alkali solution. Calcium arsenate is formed, precipitated, washed and is then ready for use as an insecticide.
U.S. Pat. No. 1,509,688, for instance, is directed toward a process for the treatment of arsenical metallurgical dusts. Dusts and fumes containing arsenic are leached with hot water, followed by extraction of the residue with a hot alkali solution. This solution is then oxidized and the arsenic is precipitated with lime.
U.S. Pat. No. 1,827,821 is directed toward a method for producing metallic lead or lead alloys from flue dust which contains lead oxide and arsenic. The flue dust is reacted with fused caustic soda to produce lead and sodium arsenate.
U.S. Pat. No. 2,951,741 provides a process for separating arsenic and sulfur from complex ores. Concentrates of the ore are treated with aerated basic solutions to form alkali metal arsenates and sulfates which are separated by reacting with lime.
U.S. Pat. No. 4,244,927 provides another process for the recovery of arsenic from materials that contain ferric-arsenic compounds which involves leaching with sodium hydroxide. Following crystallization, sodium arsenate is recovered.
Several processes are known that also provide for the recovery of bismuth from flue dusts. In U.S. Pat. No. 3,966,461, for instance, flue dust residues containing lead and silver oxides are leached with an acidic chloride leach that selectively dissolves the bismuth.
U.S. Pat. No. 4,046,687 is directed toward a process for the adsorptive removal of arsenic, antimony and bismuth from aqueous solution. A porous substrate is treated with a salt of phosphoric acid or a phosphoric acid ester. After the metals have been adsorbed, regeneration is effected with hydrochloric acid.
Finally, U.S. Pat. No. 4,244,734 is directed toward a process for recovering copper, zinc, cadmium, germanium, indium, lead, silver, gold, antimony and bismuth from flue dust containing arsenic. The arsenic is precipitated as an insoluble ferric-arsenic compound while the other metals are recovered, leaving the former in the residue. It is then converted to the soluble sodium arsenate and recovered by recrystallization.
Notwithstanding the processes and methods set forth in the foregoing art, large quantities of flue dust continue to exist and grow. The processes set forth hereinbelow, it will be seen, provide relatively simple and low cost means of treating flue dust to provide usable by-products and waste that is substantially free of useful elements as well as hazardous elements such as arsenic.